The major objective of the studies being proposed is to design HIV-1 envelope antigens that can elicit broadly reactive neutralizing antibodies (Nabs), with a long-term goal of developing a protective vaccine against the virus. We are taking a two-pronged approach of targeting gp41 membrane proximal external region (MPER) and the outer domain of gp120 (gp120OD). We have generated two prototypic antigens based on soluble form of gp41 MPER and gp1200D derived from M group consensus envelope. Both proteins can elicit Nabs against multiple primary HIV-1 isolates in mice. Our goal is to use current and evolving understanding of biochemical, structural and immunogenic properties of the prototypic antigens to design second-generation antigens that could induce even more potent Nabs. To achieve the goal, we have put together a strong, complementary, collaborative team of investigators with expertise in structural biology, virology, protein biochemistry, molecular biology, immunology and vaccinology. The specific aims of the Project 1 are: (1) to better define B cell epitopes on gp41 MPER, (2) to improve immunogenicity of neutralizing epitopes on gp41 MPER, and (3) to develop and evaluate immunogenicity of antigens based on gp120OD. Successful completion of the proposed studies would represent a major advancement towards developing a protective AIDS vaccine.